微生物および生化学技術ジャーナル

概要

Optimization of Solid State Fermentation and Leaching Process Parameters for Improvement Xylanase Production by Endophytic Streptomyces sp. ESRAA-301097

Mervat MA El-Gendy and Ahmed MA El-Bondkly

In the course of our searching program on the microbial endophytes of medical plants (Cympobogon proximus, Anethum graveolens, Artemisia judaica and Corchorus olitorius), the endophytic strain Streptomyces sp. ESRAA- 301097 derived from Cympobogon proximus proved to be the hyper xylanase producer. Screening of various locally available agro-industrial residues as substrate support for xylanase production under SSF exhibited a mixture of wheat bran (WB); sugarcane bagasse (SCB) with corncob (CC) at a ratio of 0.5:1:1 as the efficient inducer for the induction of ESRAA-301097 xylanase production as it gave the highest enzyme productivity (2364 Ugds-1) at the 4th day of fermentation when compared to individual WB, SCB or CC (1167, 1241 or 1404 Ugds-1) after 3, 4 and 4 days of incubation. Xylanase production was enhanced to 3819 Ugds-1 after optimizing the physical process parameters including temperature 30-40°C, pH 7.0, an inoculum level of 107 spore gds-1, 80-85 % initial moisture content and substrate particle size of 800 μm. An overall 23.96 % increase in enzyme production was attained with a mixture of soybean and corn steep solid as a nitrogen source but no enhancement was obtained with any of carbon or metal supplementation. Whereas xylanase yield was elucidated to 5709.2 Ugds-1 by adding Tween 20, SDS repressed its production to 750.29 Ugds-1. The optimized leaching parameters for effective extraction of xylanase (6312.45 Ugds-1) from the fermented solid mixture were found to be citrate buffer (0.1 M, pH 4.0) containing 0.2% Tween 80 as leaching agent, extractant volume 1:8 - 1:10 (w/v), soaking time 120 min, leaching pH 4 and leaching temperature 50°C under agitation at 150 rpm. The overall level of 44.61-fold purification of Streptomyces sp. ESRAA-301097 and xylanase recovery 32.52% was achieved with specific activity of 493.48 Umg-1. The purified enzyme showed a single protein band on SDS-PAGE indicating the monomeric nature of the enzyme with molecular weight ~31.5 kDa. Furthermore, whereas the inhibitors of cysteine protease (1, 10-phenanthroline and Dithiothreitol), metaloprotease (EDTA and EGTA) and thioprotease (iodoacetamide and p-chloromercuribenzoate) had no to minor effect on xylanase activity, the serine protease inhibitor (PMSF) markedly decreased it.